It's possible that your area is covered by more than one transmitter. If so, try retuning again. If that does not bring back your original BBC One region, then try a manual re-tune.
For a manual retune you need to know the channel numbers for the digital services you can receive. Go to the Digital UK website and enter your details in the postcode checker. On the results page, scroll down to the options for going digital at your address and, under Reception & channels, click on 'Find out more'. Click on 'How do I re-tune?' for full instructions.